Method of preventing ice formation and filter flugging in jet engine fuel systems



United States Patent METHOD OF PREVENTING ICE FORMATION AND FILTER PLUGGING 1N JET ENGINE FUEL SYSTEMS Theodore B. Wasserbach, Cranford, N. J., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application March 3, 1952, Serial No. 274,648

1 Claim. (Cl. 60--35.4)

This invention is concerned with an improved aviation fuel and in particular with a turbo jet-type fuel that will not plug the filters in aircraft fuel systems at relatively low temperatures. In accordance with the present invention, improved jet fuels are secured by utilizing a particular addition agent which is selected from the class of compounds represented by the formula HO(C2H40)11.H, wherein n is an integer from 3 to 8, and preferably from 4 to 6. Especially preferred compounds are tetraethylene glycol, pentaethylene glycol, and hexaethylene glycol.

The use of jet-type engines in aircraft has become increasingly widespread in the last few years. The main types of such jet engines are the turbojet, the turboprop, and the pure jet or ram jet type. In all of these engines fuel is burned with air in a set of combustors. The fuel is introduced into the combustors from a storage tank by means of suitable pumps and connecting lines. One of these pumps, located just before the combustors, is a high pressure pump and is used to inject the fuel into the various combustors at high pressures. To protect the finely machined surfaces of these pumps, micronic-type filters are positioned in the fuel lines to remove any finely divided material that may be present in the fuels employed. A major problem with respect to these micronic filters lies in the fact that they often become plugged at low temperatures with ice particles resulting from the freezing of small amounts of water dissolved or entrained in the fuels. It has now been discovered, however, that this filter plugging problem can be greatly alleviated or entirely prevented by the use of particular polyethylene glycols in the fuels.

The fuels employed in jet engines at the present time are almost entirely derived from and made up of petroleum hydrocarbons. In general, these fuels boil between 100 and 600 F., have gravities of 35 to 55 API, and possess Reid vapor pressures of 0.05 to 7 p. s. i. In this connection, the military interests have established several jet fuel specifications which exemplify very well the types of jet fuels that are being used. These fuels and their more important physical properties are listed in the 'following table:

TABLE 1 Comparzson of JP-I, JP-3, and JP-4 Turbo-fuel Specifications MIL-F-5616 MIL-F-5624A JP-l J'P-3 JP-4 Reid Vapor Pressure L1m 5-7 2-3 ASTM Disillatlon:

10% Evap. at F... Max 410 250 90% Evap. at F--. Lim 490 400 Final Bolling Pt., F. Max 572 600 550 Disillation Loss, Vol. Percent Max 1. 5 1. 5 1. 5 Total Sulfur, Wt. Percent. Max- 0. 2 O. 4 0.4 Mercaptan Sulfur, Wt. Percent Lim-. 0. 005 0. 005 Aromatics, Vol. Percent (VV-L- 791) ..MaX. 25

Bromine No., cg./grn. (VV-L-791) ax 3 30 Freezing Point, F Max-r 76 -76 76 Air Jet Residue (VV-L-79l):

Bath Temp., F Li.u1 390410 390-410 390-410 Mgs. Resid. Per 100 ml-. Max. 5 10 10 Corrosion, 3 Hrs. at 212 F ..Max 16 Hr. Accel. Gum Test: Gum, mg./

100 ml Max 20 20 Water Tolerance, m1 Lim. 2 1 1 Net Heat, Bet. u./1b Min 18, 400 18, 400 Gravity, API -Lim 45-63 40-58 1 None, 31. discoloration only. i

It will be noted that each of the specifications listed above calls for fuels having freezing points lower than 76 F. One purpose of this requirement is to combatv any fuel filter plugging due to freezing of the fuel itself at the low temperatures existing at the high' altitudes where jet aircraft normally operate. This requirement, of course, does not preclude the possibility of filter plugging caused by particles of ice which may be formed by the freezing of water that may be dissolved or entrained in a fuel.

A number of suggestions have been made for overcoming the plugging of jet fuel system filters as occasioned by the formation of ice particles. For example, it has been recommended that small amounts of compounds such as alcohols be incorporated in jet fuels. These materials, however, have been found to have a serious defiwater and fresh water.

The specific compounds that have been found to have the qualities just described are tetra-ethylene glycol, penta-ethylene glycol, and hexa-ethylene glycol. The tetra-ethylene glycol has been found to be especially effective.

Laboratory studies have established the fact that a number of polyethylene glycols are effective in reducing the filter plugging tendencies of hydrocarbon jet fuels. These studies, however, have further established the additional fact that only a limited number of these glycols are resistant to being leached from the fuel by contact with fresh or salt water. In this connection, the present in vention may be readily understood by the following example illustrating the same.

EXAMPLE A water saturated fuel of the JP-4 type described earlier containing 0.005 vol. percent dissolved Water was pumped at two different temperatures (-20 F. and 50 F.) through a micron filter and the time which elapsed before filter plugging occurred in each instance was recorded. 'The time interval at 20 F. was 9 minutes, while the time interval at 50 F. was 4 minutes. This test procedure was repeated with samples of the same water-saturated fuel to which were added 0.05 wt. percent of ethylene glycol or one of its homologs. The time required for filter plugging increased under these conditions, becoming successively longer as the molecular weight of the added polyglycol was increased. Then, to simulate practical conditions more closely, the fuel samples were stored over fresh or salt water for 24 hours and again subjected to the 20" F. filter plugging test. In other words, fuel samples containing the various glycols were run in the filter plugging test first without storing the sample over water and second after storing the same samples over water. The results of these tests are given in the following table.

TABLE 4 than others. The extent to which each polyglycol was soluble in the jet fuel is as follows:

These differences in solubility may partially account for the superiority of the tetraand hexa-ethylene glycols over the monoand di-ethylene glycols. On this basis, however, it would be expected that the nona-ethylene glycol would be the most effective of all, and such has definitely been shown not to be the case. The experimental filtering data conclusively point to a unique advantage for selected polyethylene glycols.

The value of using the tetrathrough hexa-ethylene glycols in jet fuels having been established, it should be pointed out that the amount of additive employed may vary appreciably, but should, in general, be from 0.01 to 1.0% by weight. Preferred concentrations are in the range from 0.02 to 0.5%, and particularly in the range from 0.05 to 0.10%.

These additives may be used to advantage in all types of jet fuels, but are particularly effective in the JP-l, JP-3, and JP-4 grades. They are also applicable to other fuels such as aviation gasoline for reciprocating engines and diesel fuels.

What is claimed:

A method of preventing ice formation and resultant fuel filter plugging within the fuel system of a jet propelled aircraft wherein the fuel consisting of a mixture of hydrocarbons boiling within the range from about 100 F. to 600 F. is subjected to temperatures as low as Efiect of copolymers of ethylene glycol on the low temperature filter plugging tendencies of water saturated, hydrocarbon jet fuels [JP-4 type fuel containing 0.005 vol. percent dissolved water. 0.05 wt. percent; of the copolymer added to the fuel. 10 micron fuel filten] 12. value of copolymer of general No Ad- No Adr r ula 2 4 ditlve 1 2 3 4 6 9 dltlve 3 6 9 161 1 Ter p -20 -20 20 20 20 -20 20 -50 --50 -50 --50 etc lter ug ,In ues z ase 1 g g 9 13 21 N. P. N. P N. P. N. P. 4 43 N. P. 31 Case 2 9 8 N. P 35 8 Case 2-Fuel containing copolymer stored over water for 24 hours prior to run.

The data in the above table clearly point out that ethylene glycol and copolymers of the same are very effective in reducing the filter plugging tendencies of jet fuels. It is also very apparent that all of the glycols tested with the exception of the tetrathrough the hexa-ethylene glycols are readily leached from these fuels by water. These data then established the fact that the tetra, penta-, and hexa-ethylene glycols are unique in that they not only reduce the filter plugging tendencies of jet fuels but also are extremely resistant to a leaching action occasioned by contact of such a fuel with water. The reason for the unexpected performance of these particular glycols after storage over Water is not readily apparent.

While .05 wt. percent of each polyglycol was added to the various fuel samples tested, it was noted during the C. which consists of incorporating from 0.01 wt. percent to 1.0 wt. percent of tetra ethylene glycol within the fuel.

References Cited in the file of this patent UNITED STATES PATENTS 1,696,642 Massa Dec. 25, 1928 2,499,551 White Mar. 7, 1950 2,563,101 Colwell et a1. Aug. 7, 1951 2,563,305 Britton et a1. Aug. 7, 1951 FOREIGN PATENTS 333,200 Great Britain Dec. 29, 1930 OTHER REFERENCES Murray: Aircraft Gas-Turbine-Fuels, The Oil and Gas Journal (March 29, 1951), pages 218, 219, 271-281.

tests that some polyglycols were noticeably less soluble Copy in Scient. Lib. 

